134 PART I. GENERAL ACCOUNT 



common with that of the Annelida than with that of the Deuterostomia. In 

 the Pogonophora the gonads are closely bound up with the coelomic walls 

 and the germinal cells occupy a retroperitoneal position. In the female the 

 eggs tumble out into the coelom through rupture of the coelomic wall of the 

 ovary. In the male, maturation of the germ cells takes place in the sperm sacs, 

 i.e. in essence in the coelom also. The genital products are passed to the 

 exterior from the coelom through the coelomoducts. These are all characters 

 which are shared with the annelids. 



In Hemichordata and Acraniata, on the contrary, the gonads are separated 

 from the general body cavity. It is, however, well known that the gonocytes 

 in these animals too make their first appearance retroperitoneally and only 

 later are the genital organs cut off from the coelom (Spengel, 1893; Zarnik, 

 1905). In the Echinodermata also the genital primordium is developed in 

 association with the coelom. Finally, in the vertebrates the gonad is formed 

 on the wall of the common coelomic cavity and the genital products fall into 

 the coelom. Thus no significant distinction exists in those aspects which 

 interest us between the genital apparatus of the annelids and the deutero- 

 stomic phyla. It is a mark of their extremely primitive condition that the 

 gonad in the Pogonophora is not separated from the coelom, and in this 

 sense they are formally nearer to the annelids than to the Hemichordata, but 

 at the same time they stand on a par with the vertebrates. The similarity with 

 the vertebrates is perhaps a reflexion of their common possession of trunk 

 coelomoducts through which the genital products are discharged from the 

 coelom. 



Thus it is clear that in the question of the phylogenetic position of the 

 Pogonophora the genital system gives no grounds for prefering annelid 

 relationships over deuterostomic. 



Are they related to the Phoronidea ? 



The question whether the Pogonophora might be related to the Phoro- 

 nidea was raised by Johansson (1937, 1939), who immediately answered his 

 own question in the negative. To our eyes the differences between the groups 

 are more profound than Johansson showed. We may note the principle 

 differences, looking first at the promorphological distinctions. 



It is well known that the body of Phoronis is first formed as an outgrowth 

 from the antero-ventral surface of the actinotroch larva, i.e. the Phoronidea 

 are true Podaxonia (in the sense of Ray Lankester) and the adult body is not 

 in any sense comparable with the body of such protaxonal animals as the 

 Pogonophora. But if, nevertheless, we do compare the various organ systems 



